Note 176 — MEMOIR OF THE LIFE OF DAVID RITTENHOUSE; CONTINUED, FROM THE TIME OF HIS SETTLEMENT IN PHILADELPHIA.

“In order to carry on the parallel of latitude with as much expedition and economy as possible,” says Mr. Ellicott, “we dispensed with the method of tracing a line on the arc of a great circle, and correcting into the parallel; as pursued by Messrs. Mason and Dixon, in determining the boundary between this state” (Pennsylvania,) “and the state of Maryland, and which we followed in completing their line in the year 1784. We commenced our operations by running a guide-line, West, with a surveying compass, from the point mentioned on the Delaware” (the one which was fixed by Dr. Rittenhouse and Capt. Holland, in the year 1774,) 20¼ miles; and there corrected by the following zenith lines” (laid down in the sequel,) “taken, at its western termination, by a most excellent Sector, constructed and executed by Dr. Rittenhouse.”